Lithography technique used electron beam, ion beam or other charged particle beam has been developed as next generation lithography. In forming a mask used to the lithography technique, a mask blank (a substrate to be mask) is deeply etched from its reverse surface side to form a thin film region (a membrane) of almost 10 nm to 10 μm thickness and then a pattern to be projected is arranged in the membrane.
Since the mask has a membrane region in lower mechanical rigidity, a method forming a pattern in high placement precision and additionally a method measuring mask strain to correct a placement error by applying with measured data are important.
For example, Electron-beam Projection Lithography (EPL) is used with a stencil mask having a beam structure, and it has been proposed that a mark formed on the beam is measured by a laser interference coordinate measurement apparatus and the measured mask strain is corrected by an electro-optical system.
However, in explanation blow, an influence of the mask deformation caused by gravity is not considered. Further, if an influence of gravity is calculated with respect to the measured mask strain data by a numeric processing, it may not be considered that a difference in the mask shape, a reappearance in a fixing method, or a difference in fixing methods of the mask by the coordinate measurement apparatus and by the exposure apparatus.
On the other hand, in Proximity X-ray Lithography (PXL), a method to correct a mask deformation at the time of an EB description has been proposed (refer to The Japanese Unexamined Patent Publication (Kokai) No. 8-203817).
However the method has to form two masks, so that it is not desirable in terms of production time, handling and cost. Considering yield of a PXL mask, several or more test may have to be performed repeatedly in order to form a single mask. In actual, a production of the PXL mask by this method has not been popularized.
In photolithography, although the mask deformation caused by gravity has been recognized (refer to The Japanese Unexamined Patent Publication (Kokai) No. 6-18220), only improvement of a mask-fixing method or other improvement of hardware has been proposed.